This invention relates to a ballasting component for a discharge device and, more particularly, to a composite structure for use as an HID device ballasting component which performs the dual functions of voltage transformation and provision of ballasting inductive reactance which can be controllably shifted in value.
Discharge devices normally require some type of ballasting or current limiting feature in order to prevent a runaway discharge due to the negative volt-ampere characteristics of such devices. In recent years the use of so-called high-pressure sodium or sodium-mercury lamps has expanded greatly because of the high efficiency and long life which can be obtained with such lamps. These lamps normally display a rising voltage characteristic throughout lamp life. Unless some provision is made to control the power input to the lamp, this rising voltage characteristic will reflect in increased wattage input into the lamp which, if it is not controlled within predetermined limits, can impair the performance of the lamp. The performance of such lamp can also be adversely affected by line voltage variations which are reflected as substantially increased or decreased power consumption by the operating lamp.
In U.S. Pat. No. 4,162,429, dated July 24, 1979 to Elms et al. is disclosed a ballast circuit which accurately regulates the wattage drawn by an operating HID lamp and particularly a so-called high-pressure sodium lamp. This circuit senses both the line voltage and lamp voltage in order to close a bilateral switch at a variable but predetermined time in each half cycle of AC energizing potential. The switch on closing serves to close a control winding in a variable inductance device such as is disclosed in U.S. Pat. No. 4,162,428, dated July 24, 1979 to Elms. While this combination of control circuit and variable inductor works very effectively, some separate type of voltage transformation is needed unless the device is to be operated across a 240 volt or higher voltage line.
U.S. Pat. No. 3,873,910, dated Mar. 25, 1975 to Willis, Jr. disclosed a variable inductor which includes a main winding and a control winding positioned on opposite sides of a gapped shunt. The control winding is adapted to be closed by a gate-actuated AC switch, and upon closing, the inductance of the variable inductor is decreased by a predetermined amount, thereby controlling the power input to the ballasted lamp. U.S. Pat. No. 4,037,148, dated July 19, 1977 to Owens disclosed a ballast device especially adapted to operate with a variable inductor as described in the foregoing U.S. Pat. No. 3,873,910 to ballast a high-pressure sodium-discharge lamp wherein a non-linear amplifier is incorporated in circuit. For actual control, lamp voltage and line voltage are sensed and these voltage signals are combined in a programmable uni-junction transistor to control the firing time thereof, and thus the actuation of the gate-controlled switch. Such a circuit normally provides voltage transformation by means of an auto-transformer.
Various other types of sensing and control circuits are known and U.S. Pat. No. 3,590,316, dated June 29, 1971 to Engel et al. discloses a transistorized watt-meter which is used to control the duty cycle or to vary an impedance in order to control lamp wattage.